A complete Debian GNU/kFreeBSD system should work within a jail, on a GNU/kFreeBSD or regular FreeBSD host system, with a few limitations.
Jails work a lot like Linux OpenVZ. On the host you can see all processes running in all jails. Within a jail, you can only see the processes running in that jail.
Be aware that some files in /proc or /sys, such as /proc/mounts, are not namespaced per jail, and this may leak some (read-only) information about the host, or other guests' mountpoints.
Some features such as sysvipc share a single namespace with the host and other jails, so for security reasons it is disabled by default. fakeroot requires it to be enabled. Running more than one postgresql-server instance in a shared sysvipc namespace would clash, and not normally work.
The raw_sockets feature is normally disabled, to prevent IP spoofing from inside the jail. The ping tool will not work properly as a result.
Creating a new jailed system
JID=101 MIRROR="http://http.debian.net/debian" debootstrap \ --exclude=devd,dmidecode,isc-dhcp-client,isc-dhcp-common,kldutils,pf,vidcontrol \ wheezy /srv/jail/$JID "$MIRROR" HOSTNAME=jail$JID.example.com IP=10.1.0.$JID echo "$HOSTNAME" > /srv/jail/$JID/etc/hostname echo "$IP $HOSTNAME" >> /srv/jail/$JID/etc/hosts
The --exclude to debootrap lists some packages that are probably not useful in a jailed system. The devd package will typically not work in a jail.
Ensure the jailed system's /etc/resolv.conf is suitable. If a DNS resolver runs on the host system, you should reference it by unicast (public or private) IP address such as "nameserver 10.1.0.1", instead of e.g. "nameserver 127.0.0.1".
The jailed system will not have a loopback interface unless you create one.
Starting or stopping a jail
ATTENTION: Earlier versions of this Wiki page did not explain the necessary devfs setup to restrict the set of devices in /dev. See the advisory for a similar issue at http://security.freebsd.org/advisories/FreeBSD-SA-14:07.devfs.asc
TODO: upstream FreeBSD configures on boot a restricted ruleset 4, suitable for jailed systems. This is not packaged yet for Debian GNU/kFreeBSD but you can initialise it manually; you only need to do this once per boot of the host system (not for every jail creation).
while read RULE ; do devfs rule -s 4 add $RULE ; done <<EOF hide path log unhide path null unhide path zero unhide path crypto unhide path random unhide path urandom unhide path ptyp* unhide path ptyq* unhide path ptyr* unhide path ptys* unhide path ptyP* unhide path ptyQ* unhide path ptyR* unhide path ptyS* unhide path ptyl* unhide path ptym* unhide path ptyn* unhide path ptyo* unhide path ptyL* unhide path ptyM* unhide path ptyN* unhide path ptyO* unhide path ttyp* unhide path ttyq* unhide path ttyr* unhide path ttys* unhide path ttyP* unhide path ttyQ* unhide path ttyR* unhide path ttyS* unhide path ttyl* unhide path ttym* unhide path ttyn* unhide path ttyo* unhide path ttyL* unhide path ttyM* unhide path ttyN* unhide path ttyO* unhide path ptmx unhide path pts unhide path pts/* unhide path fd unhide path fd/* unhide path stdin unhide path stdout unhide path stderr unhide path ptyp* unhide user root group root EOF
FIXME: this devfs ruleset breaks the method of PTY allocation used by wheezy chroots; ssh logins will warn of "PTY allocation request failed on channel 0", have no shell prompt, and likely have other issues. This additional rule seems to fix it (no idea why, and don't know if it's secure) :
path pt* unhide
sid/jessie chroots don't need that - they use a new method of pty allocation which unaffected.
Assuming a debootstrap'd installation already exists in /srv/jail/$JID/, here is an example of how to start it up inside a jail:
JID=101 # Linux-like /proc and /sys filesystems mount -t linprocfs linprocfs /srv/jail/$JID/proc mount -t linsysfs linsysfs /srv/jail/$JID/sys # Ramdisk required for /run mount -t tmpfs tmpfs /srv/jail/$JID/run # A read-only /dev filesystem with restricted set of devices mount -t devfs devfs /srv/jail/$JID/dev mount -t fdescfs fdescfs /srv/jail/$JID/dev/fd # :XXX: ruleset 4 must be initialised as explained earlier in this Wiki page devfs -m /srv/jail/$JID/dev rule -s 4 applyset # Ensure the jail has some essential devices for DEVICE in null random urandom zero do if [ ! -e /srv/jail/$JID/dev/$DEVICE ] then echo "error: device '/dev/$DEVICE' MUST be available in the jail" exit 1 fi done # Ensure the jail has only a limited set of devices for DEVICE in mem kmem do if [ -e /srv/jail/$JID/dev/$DEVICE ] then echo "error: device '/dev/$DEVICE' MUST NOT be available in the jail" exit 1 fi done # Compatibility symlink from /dev/shm to /run/shm ln -s /run/shm /srv/jail/$JID/dev/ # Optionally enable networking HOSTNAME=jail$JID.example.com # :XXX: this IP address *must* be assigned to one of the host's interfaces before the guest can use it IP=10.1.0.$JID mkdir -p /var/run/jail jail -J /var/run/jail/$JID.jid -c jid=$JID \ name=jail$JID \ path=/srv/jail/$JID \ host.hostname=$HOSTNAME \ ip4.addr=$IP \ command=/bin/sh -- -c "/etc/init.d/rc S && /etc/init.d/rc 2"
You may want to install and configure locales on the first boot:
apt-get install locales dpkg-reconfigure locales
If openssh-server is installed within the jail, you should be able to SSH into it like a virtual private server.
jls (to list running jails) is not available yet. 709225
jexec is not available yet, but you can probably get by with:
# jail -m jid=$JID command=/bin/bash # cd
A jail stops 'running' when all processes within it exit. (Within the jail, /etc/init.d/rc 0 ; exec kill -1 might be a way to force a shutdown?)
The libjail package was not distributed with Squeeze. The kernel functionality has existed since FreeBSD 4.x however, so it may work if you can build the necessary userland tools.